The widespread occurrence of antibiotic resistance among bacteria is causing increasing concern as a major public health threats. Current antibiotics cause death or growth arrest in the target bacteria. As a result, antibiotic use exerts strong selective pressure to favor antibiotic resistant strains. Novel antimicrobial reagents that suppress pathogen virulence without selecting for antibiotic resistance provide a promising alternative approach for treatment of infectious diseases. Group A Streptococcus (GAS) is an important human pathogen affecting millions of people globally each year. The streptokinase (SK) is a major GAS virulence factor that activates human plasminogen. In our previous studies, we have established the streptokinase/plasminogen interaction as a critical factor in GAS pathogenesis. We propose to take advantage of this observation and design novel antimicrobial reagents for the treatment of GAS infection. In the preliminary study, we have screened 55,000 small compounds for inhibitors of SK expression in GAS and 23 candidate hit compounds have been identified. An additional high throughput screen of up to 500,000 more small compounds for SK expression inhibitors is proposed by taking advantage of the NIH Molecular Libraries and Imaging roadmap initiative. A growth based screen will be optimized to use a GAS strain with kanamycin resistance gene under control of SK promoter to screen for small compounds that can inhibit kanamycin resistance expression, which will serve as lead compounds for SK expression inhibitors. In the future, global effects of candidate compounds on GAS gene expression will be studied to provide clues for identification of the targets. Two GAS two-component systems that have been demonstrated to regulate SK expression in published reports will be tested as prime candidate targets. In addition, a number of murine GAS infection models established in our previous studies will be used to elucidate the effects of candidate compounds on GAS virulence in vivo. Data collected from the above studies will further our understanding of the contribution of SK to GAS infection and identify small compounds that can inhibit GAS virulence. As a result, alternative approach to treat bacterial infection by interfering with GAS virulence without unduly introducing selection pressure for resistance can be explored to supplement antibiotic treatment. [unreadable] [unreadable] [unreadable]